Supported catalysts

ABSTRACT

Supported catalyst particles, which can be incorporated in the tobacco cut filler, cigarette wrapper and/or cigarette filter of a cigarette, are useful for low-temperature and near-ambient temperature catalysis of carbon monoxide and/or nitric oxide. The supported catalyst comprises catalyst particles that are supported on particles of an electrically conductive support selected from the group consisting of graphitic carbon and a partially reduced oxide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.provisional Application No. 60/749,593, filed on Dec. 13, 2005, theentire content of which is incorporated herein by reference.

BACKGROUND

Cigarettes produce both mainstream smoke during a puff and sidestreamsmoke during static burning. Constituents of both mainstream smoke andsidestream smoke are carbon monoxide (CO) and nitric oxide (NO). Thereduction of the amount of carbon monoxide and/or nitric oxide in smokeis desirable.

SUMMARY

A preferred embodiment of a component of a cigarette comprises particlesof a supported catalyst, wherein the supported catalyst comprisescatalyst particles supported in and/or on electrically conductivesupport particles of graphitic carbon or a partially reduced oxide. Thecomponent is selected from the group consisting of tobacco cut filler,cigarette paper and cigarette filter material.

A preferred embodiment of a cigarette comprises a tobacco rod, cigarettepaper and an optional filter. At least one of the tobacco rod, cigarettepaper and optional filter comprises supported catalyst particles for theconversion of carbon monoxide to carbon dioxide and/or nitric oxide tonitrogen. The supported catalyst particles comprise catalyst particlessupported in and/or on electrically conductive support particlesselected from the group consisting of graphitic carbon and a partiallyreduced oxide.

Also disclosed is a preferred method of making a cigarette comprisingincorporating supported catalyst particles in and/or on at least one oftobacco cut filler, a cigarette wrapper optionally comprising web-fillermaterial and a cigarette filter comprising filter material; forming atobacco column from the tobacco cut filler in a cigarette makingmachine; and placing the cigarette wrapper around the tobacco column toform a tobacco rod of a cigarette; and optionally attaching thecigarette filter to the tobacco column using tipping paper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary smoking article having supported catalystparticles supported on tobacco cut filler with a magnified view of thetobacco cut filler.

FIG. 2 shows an exemplary smoking article having supported catalystparticles supported on the web of a wrapper with a magnified view of thewrapper.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Disclosed are particles of a supported catalyst that can be incorporatedinto a component of a cigarette. The supported catalyst particles, whichcomprise catalyst particles that are incorporated in and/or on particlesof an electrically conductive support, can be incorporated into one ormore components of a cigarette such as tobacco cut filler, cigarettepaper and/or cigarette filter material. In a preferred embodiment, thesupported catalyst particles are incorporated in an amount effective toconvert carbon monoxide to carbon dioxide and/or convert nitric oxide tonitrogen during smoking of the cigarette. Exemplary support particlescomprise graphitic carbon or at least one partially-reduced oxide. Thesupported catalyst is useful for low-temperature or near-ambienttemperature catalysis of carbon monoxide and/or nitric oxide. Byincorporating the supported catalyst into a component of a cigarette,the amount of carbon monoxide and/or nitric oxide in mainstream smokecan be reduced.

The supported catalyst particles may also reduce the concentration inmainstream smoke of at least one polyaromatic hydrocarbon compound. Forexample, the supported catalyst particles may reduce the concentrationin mainstream smoke of at least one of naphthalene, acenaphthene,fluorene, phenanthrene, anthracene, fluoranthrene, pyrene,benz(a)anthracene, chrysene, benzo(b)fluoranthrene,benzo(k)fluoranthrene, benzo(a)pyrene, indeno[1,2,3-cd]pyrene,dibenz[a,h]anthracene and benzo[g,h,i]perylene.

Particles of the catalyst and particles of the support preferably havelow aspect ratio shapes such as spheres. However, these particles mayalso include higher aspect ratio shapes, such as fibers. The particlesof the catalyst and/or the particles of the substrate may have an aspectratio of about 1 (e.g., spheres) or greater than 1 (e.g., whiskers orfibers) where the “aspect ratio” is defined as the ratio of length todiameter of a particle.

The catalyst particles can comprise particles of a metal or a metaloxide. For example, the catalyst particles can comprise particles of anoble metal or a noble metal oxide. The catalyst particles can comprisenanoscale particles. By “nanoscale” is meant that the particles have anaverage particle diameter of less than a micron (e.g., less than about100 nm, more preferably less than about 50 nm, and most preferably lessthan about 10 nm).

Preferred catalyst particles are iron oxide particles. Non-porousnanoscale iron oxide particles are marketed by MACH I, Inc., King ofPrussia, Pa. under the trade names NANOCAT® Superfine Iron Oxide (SFIO)and NANOCAT® Magnetic Iron Oxide. The NANOCAT® Superfine Iron Oxide isamorphous ferric oxide in the form of a free flowing powder, with aparticle size of about 3 nm, a specific surface area of about 250 m²/g,and a bulk density of about 0.05 g/cm³. The NANOCAT® Superfine IronOxide is synthesized by a vapor-phase process, which renders itsubstantially free of impurities, and is suitable for use in food,drugs, and cosmetics. The NANOCAT® Magnetic Iron Oxide is a free flowingpowder with a particle size of about 25 nm and a surface area of about40 m²/g. The support particles can comprise one or more metal oxides.

The support particles are electrically conductive. The support particlespreferably enhance the catalytic, oxidative and/or reducing propertiesof the catalyst particles. The support particles themselves may havecatalytic activity. In a first embodiment, the support particlescomprise graphitic carbon. In a second embodiment, the support particlescomprise particles of at least one partially-reduced metal oxide.

Preferred support particles comprise graphitic carbon nanostructures,such as graphite nanotubes or graphite nanofibers. Graphite nanotubesand graphite nanofibers are comprised of graphite sheets that arealigned in a direction ranging from substantially perpendicular tosubstantially parallel to the longitudinal (or growth) axis of thenanostructure. Graphite nanotubes and nanofibers can also have adiameter from about 0.5 nm to 1,000 nm, preferably from about 1 to 500nm. Graphitic substrates preferably have a surface area of from about 1to 4,000 m²/g, more preferably from about 100 to 1000 m²/g, and acrystallinity of from about 50% to 100%, more preferably from about 90%to 100%.

Graphite support particles can be obtained commercially or formed by anysuitable process. Supported catalyst particles may be formed bycombining commercially available graphite support particles withcatalyst particles or with a precursor compound that can be processed(e.g., thermally decomposed) to form catalyst particles.

Commercially available graphite nanotubes, for example, typicallycomprise incorporated therein metallic catalyst particles such as cobaltparticles or nickel particles. A catalyst such as cobalt or nickel istypically used during the manufacture of the graphite nanotubes, andmetallic particles of the catalyst can remain incorporated in thegraphite nanotubes after they are formed. Even though the catalystparticles are enveloped by the graphite (i.e., the metallic catalystparticles are typically not exposed to a gas stream passing over thegraphite nanotubes), the catalytic activity of graphite nanotubes can beenhanced with respect to graphite nanotubes that are free of catalystparticles. An electron transfer mechanism between the catalyst particlesand the graphite substrate can explain the catalytic enhancement.

In a further method, graphitic support particles can be prepared viamelt-, dry- or wet-spinning of one or more suitable carbon precursorssuch as (poly)acrylonitrile, petroleum pitch, phenolic resins or othersuitable polymers. In a preferred method, electrospinning can be used tosynthesize graphitic support particles. In electrospinning, anelectrostatic force is used to eject a continuous charged jet of apolymer solution (or melt) through an orifice. Graphitic fibers can beformed via curing and pyrolysis of green fibers formed from the ejectedsolution. Electrospinning can be used to prepare fibrous graphiticparticles having a diameter ranging from several nanometers to severalmicrons.

An electrospinning apparatus can comprise means such as a syringe pumpfor metering a polymeric solution at a desired liquid flow rate. Avoltage can be applied to the output orifice of the syringe pump. Theapparatus can further comprise a grounded target, which is preferablyadapted to rotate and/or translate with respect to the output orifice ofthe syringe pump. A fixed distance can be maintained between the outputof the syringe pump and the target.

By way of example, substrate particles comprising graphite nanotubes andgraphite nanofibers can be prepared by electrospinning polymersolutions. A first exemplary polymer solution comprises a 50 wt. %/wt. %solution of Novolak phenolic resin dissolved in ethanol. A secondexemplary polymer solution comprises a 50 wt. %/wt. % solution of Resolephenolic resin dissolved in ethanol. Suitable polymer solutions may havea concentration greater than or less than 50 wt. % (e.g., about 10, 20,30, 40, 50, 60, 70, 80 or 90±5 wt. %, but preferably in the range ofabout 35 to 55 wt. %). Graphite fibers can be formed from a polymersolution comprising a single resin or a mixture of resins. Furthermore,the polymer solution can further comprise an additive such as catalystparticles or one or more precursors thereof. Novolak and Resole phenolicresins are commercially available from Durez Corporation, Addison, Tex.

The volumetric flow rate of a resin solution can be from about 0.1-50ml/hr, preferably from about 5 to 20 ml/hr; the voltage applied to theoutput of the device for metering the resin solution can be from about 1to 50 keV, preferably from about 10 to 20 key; and the distance betweenthe output of the metering device and the target can be from about 5 to50 cm, preferably from about 10 to 20 cm. Green fibers can be cured at afirst temperature (e.g., between about 100° C. and 200° C.) andpyrolyzed to form graphite at a second temperature greater than thefirst temperature (e.g., between about 300° C. and 2000° C.).

For fibers spun from ethanol solutions of the Novolak and Resolephenolic resins, a preferred curing temperature is about 160° C., and apreferred pyrolysis temperature is between about 1600° C. and 2000° C.Fibers are preferably cured and pyrolyzed in an inert (e.g.,non-oxidizing) atmosphere. For example, spun fibers can be cured and/orpyrolyzed in a vacuum furnace in an atmosphere of flowing argon ornitrogen.

Generally, the porosity of pyrolyzed graphite fibers decreases withincreasing pyrolysis temperature. Furthermore, fibers pyrolyzed athigher temperatures typically display a more ordered crystallographicalignment of graphite sheets than fibers pyrolyzed at lowertemperatures. The surface area of electrospun fibers pyrolyzed at atemperature of between about 400° C. and 1600° C. is between about 250and 650 m²/g, while the surface area of electrospun fibers pyrolyzed ata temperature of between about 1600° C. and 2000° C. is less than about30 m²/g.

Catalyst particles can be incorporated in electrospun graphite fibers byincorporating catalyst particles or a catalyst precursor into the resinthat is spun. In a first example, catalyst particles (e.g., nanoscaleiron oxide particles) can be incorporated into the resin. In a secondexample, a catalyst precursor (e.g., a copper, cobalt or platinumprecursor) can be incorporated into the resin solution. According to thesecond example, during curing and/or pyrolysis of the green fibers toform graphite fibers, catalyst particles can form in situ via thermaldecomposition of the catalyst precursor. Incorporation of a metal, metaloxide or precursor compound into the resin solution used forelectrospinning may promote formation of graphite at lower pyrolysistemperatures than resin solutions that are metal, metal oxide orprecursor compound free.

According to another preferred embodiment, the support particles cancomprise a partially-reduced metal oxide. The partially-reduced metaloxide preferably comprises a Magnéli phase (i.e., substoichiometricoxide) of titanium, vanadium, chromium, zirconium, niobium, molybdenum,hafnium or tantalum. Optionally, the sub-stoichiometric oxide can bedoped. The dopant, which is different than the metal constituting themetal oxide, can be titanium, vanadium, chromium, zirconium, niobium,molybdenum, hafnium or tantalum.

Without wishing to be bound by any particular theory, it is believedthat the addition of a dopant can stabilize the sub-oxide. A preferreddopant that can be added to titanium oxide-based support particles is,for example, niobium. The dopant addition can stabilize the sub-oxide(e.g., inhibit re-oxidation of the partially reduced oxide). Dopant-freesub-oxides (e.g., Ti₄O₇) more readily re-oxidize than doped sub-oxidephases. The catalytic efficiency of supported catalyst particlescomprising re-oxidized support particles TiO₂) is less than thecatalytic efficiency of supported catalyst particles comprising asubstoichiometric oxide support.

Substoichiometric oxides (e.g., Magnéli phases) can be represented bythe chemical formula(s) M_(n)O_(2n-1), or M_(n)O_(3n-1), (4≦n≦20), whereM is a transition metal. M is preferably one of Ti, V, Cr, Zr, Nb, Mo,Hf and Ta. Magnéli phases have a crystallographic structure similar to,but distinguishable from, the rutile structure of triclinic titaniumdioxide. Magnéli phases are substoichiometric, that is, they are oxygendeficient with respect to the valence requirements of stoichiometricmetal oxides having the rutile structure (e.g., TiO₂). To accommodatethe oxygen deficiency, Magnéli phases comprise a lattice distortion.Magnéli phases comprise two or more two-dimensional arrays of MO₂octrahedra that are spaced apart by shear planes having thestoichiometry MO. The localized shear planes can provide a conductivepathway for the transfer of electrons. The most conductive Magnélistructure is the most reduced phase (M₄O₇), which has the highestdensity of shear planes.

Magnéli phase titanium sub-oxide materials are disclosed in Magnéli, A.Acta Chem. Scand., 13, 989 (1959), the entire content of which is herebyincorporated by reference.

Magnéli phase sub-oxides can be prepared by heating stoichiometricoxides at a temperature in excess of about 1000° C. in a reducingatmosphere. For example, support particles of titanium oxide (e.g.,Ti₄O₇) can be prepared by heating commercially available powders oftitania (TiO₂) at about 1200° C. for up to about 2 weeks (e.g., fromabout 1, 2 or 3 hours to about 200 or 500 hours) in flowing hydrogen,nitrogen, argon or mixtures thereof. An exemplary gas flow rate is about1 liter/min., though lower or higher gas flow rates can be used.

The support particles, which can be nanoscale particles or larger (e.g.,micron-sized) particles, preferably have an average particle size ofless than about 10 microns, though more preferred support particles havean average particle size of less than about 1 micron (e.g., less thanabout 0.5 micron or less than about 0.1 micron).

The support particles (i.e., graphite particles or sub-oxide particles)can comprise porous or non-porous particles. Pores with diameters lessthan about 20 nm are commonly known as micropores. Pores with diametersbetween about 20 and 500 nm are known as mesopores, and pores withdiameters greater than about 500 nm are defined as macropores. Thecatalyst particles can be supported on an external surface of thesupport particles or within the channels and pores of porous supportparticles such as carbon nanotubes. The catalyst particles can becompletely enveloped by the matrix of the support particles.

The support particles can act as a separator, which can inhibitdiffusion, agglomeration or sintering together of the supported catalystparticles before or during combustion of the cut filler and/or cigarettepaper during smoking. Because a support can minimize sintering of thecatalyst particles, it can minimize the loss of their active surfacearea. The catalyst particles can be chemically or physically bonded tothe support particles.

The support particles are preferably characterized by a BET surface areagreater than about 20 m²/g, e.g., from about 50 m²/g to 2,500 m²/g,optionally with pores having a pore size greater than about 3 Angstroms,e.g., from about 10 Angstroms to 10 microns.

By “incorporated in” is meant that the catalyst particles are dispersedat least partially throughout the matrix of the support particles. By“incorporated on” is meant that the catalyst particles are dispersed onat least a portion of an exposed surface of the support particles.

Preferred supported catalyst particles comprise nanoscale catalystparticles supported on particles of graphitic carbon or apartially-reduced oxide.

The sub-oxides of titanium, vanadium, chromium, zirconium, niobium,molybdenum, hafnium and tantalum can act both as a support in synergywith the catalyst particles and as an active metal oxide oxidationcatalyst. Equilibrium between different oxidation states of theprincipal metal (e.g., Ti²⁺ and Ti⁴⁺) can result in an exceptionallyhigh oxygen storage and release capacity that enables catalyticcombustion of CO by providing oxygen directly to catalytically activesites.

Catalyst particles can be incorporated in the support particles byvarious methods such as by physically admixing the catalyst particleswith the support particles and/or via chemical routes such as by formingthe catalyst particles in situ.

In one method, substantially dry catalyst particles can be physicallyadmixed with support particles and the mixture can be agitated toincorporate the catalyst particles in and/or on the support particles.The catalyst particles can be chemically or physically bonded to anexposed surface of support particles (e.g., an external surface and/or asurface within a pore of cavity).

In a further method, catalyst particles may be dispersed in a liquid,and support particles may be mixed with the liquid having the dispersedcatalyst particles. Catalyst particles dispersed in a liquid can becombined with support particles using techniques such as spraying orimmersion.

After combining the support particles with the dispersed catalystparticles, the liquid can be removed (e.g., by evaporation) leaving thesupported catalyst particles incorporated in and/or on the supportparticles. The liquid, which can be used to promote infiltration and/oradhesion of the catalyst particles to the support particles, may besubstantially removed by heating the catalyst particle-supportparticle-liquid mixture at a temperature higher than the boiling pointof the liquid and/or by reducing the pressure of the atmospheresurrounding the mixture. Any suitable liquid can be used to form adispersion of the catalyst particles, including, but not limited towater, alcohols and mixtures thereof.

It will be appreciated that supported catalyst particles can be formedby forming a dispersion of the support particles and combining thedispersed support particles with catalyst particles.

In yet a further method, catalyst particles can be formed in situ inand/or on the support particles via the decomposition (.g., thermaldecomposition) of at least one suitable catalyst precursor compound.Supported catalyst particles can be formed by combining a catalystprecursor with already-formed support particles or, as disclosed above,with a precursor used to form the support particles (e.g., a polymerresin) and then by thermally treating the mixture to form catalystparticles that are incorporated in and/or on the support particles.

The mixing of support particles with at least one catalyst precursor canbe performed at about ambient temperature or at elevated temperatures,e.g., through reflux. The thermal treatment used to decompose thecatalyst precursor(s) can be carried out in various atmospheres. Forinstance, a mixture comprising the support particles and at least onecatalyst precursor can be heated in an inert, reducing or oxidizingatmosphere to form the catalyst particles.

An inert atmosphere suitable for thermally decomposing a catalystprecursor compound can comprise, for example, helium, argon, or mixturesthereof. A reducing atmosphere can comprise hydrogen, nitrogen ormixtures thereof. An oxidizing atmosphere can comprise oxygen (e.g.,air).

In embodiments where catalyst particles are formed from thermaldecomposition of a catalyst precursor, preferably the catalyst precursoris heated to a temperature equal to or greater than its decompositiontemperature. The preferred temperature will depend on the particularligands used. The decomposition temperature of the catalyst precursor isthe temperature at which the ligands substantially dissociate (orvolatilize) from the metal atoms. During this process the bonds betweenthe ligands and the metal atoms are broken such that the ligands arevaporized or otherwise separated from the metal. Preferably all of theligands decompose. However, catalyst particles made using a catalystprecursor may contain carbon obtained from partial decomposition of theorganic or inorganic components present in the catalyst precursor and/orsolvent used to form a catalyst precursor solution.

The catalyst precursor compounds preferably are high purity, non-toxic,and easy to handle and store (with long shelf lives). Desirable physicalproperties include solubility in solvent systems, compatibility withother precursors and volatility for low temperature processing.

The catalyst precursor compounds are preferably metal organic compounds,which have a central main group, transition, lanthanide, or actinidemetal atom or atoms bonded to a bridging atom (e.g., N, O, P or S) thatis in turn bonded to an organic radical. Such compounds may includemetal alkoxides, β-diketonates, carboxylates, oxalates, citrates, metalhydrides, thiolates, amides, nitrates, carbonates, cyanates, sulfates,bromides, chlorides, and hydrates thereof. The catalyst precursor canalso be a so-called organometallic compound, wherein a central metalatom is bonded to one or more carbon atoms of an organic group. Aspectsof processing with these catalyst precursors are discussed below.

Metal alkoxides M(OR)_(n) possess both good solubility and volatilityand are readily applicable to MOD processing. Metal alkoxides reacteasily with the protons of a large variety of molecules. This allowseasy chemical modification and thus control of stoichiometry by using,for example, organic hydroxy compounds such as alcohols, silanols(R₃SiOH), glycols OH(CH₂)_(n)OH, carboxylic and hydroxycarboxylic acids,hydroxyl surfactants, etc.

Metal β-diketonates [M(RCOCHCOR′)_(n)]_(m) are attractive catalystprecursors because of their volatility and high solubility. Theirvolatility is governed largely by the bulk of the R and R′ groups aswell as the nature of the metal, which will determine the degree ofassociation, m, represented in the formula above. Acetylacetonates(R═R′═CH₃) are advantageous because they can provide good yields.

Metal β-diketonates are prone to a chelating behavior that can lead to adecrease in the nuclearity of these precursors. These ligands can act assurface capping reagents and polymerization inhibitors. Thus, smallparticles can be obtained after hydrolysis ofM(OR)_(n-x)(β-diketonate)_(x). Acetylacetone can, for instance,stabilize nanoscale colloids. Thus, metal β-diketonate precursors arepreferred for preparing nanoscale catalyst particles.

Metal carboxylates such as acetates (M(O₂CMe)_(n)) are commerciallyavailable as hydrates, which can be rendered anhydrous by heating withacetic anhydride or with 2 methoxyethanol. Many metal carboxylatesgenerally have poor solubility in organic solvents and, becausecarboxylate ligands act mostly as bridging chelating ligands, readilyform oligomers or polymers. However, 2 ethylhexanoates(M(O₂CCHEt_(n)Bu)_(n)), which are the carboxylates with the smallestnumber of carbon atoms, are generally soluble in most organic solvents.

The use of multiple single-catalyst precursors has the advantage offlexibility in designing precursor rheology as well as catalyststoichiometry. Hetero-metallic precursors, on the other hand, may offeraccess to metal systems whose single catalyst precursors haveundesirable solubility, volatility or compatibility.

Mixed-metal (i.e., hetero-metallic) species can be obtained via Lewisacid-base reactions or substitution reactions by mixing alkoxides and/orother catalyst precursors such as acetates, β-diketonates or nitrates.The combination reactions are typically controlled by thermodynamics;however, the stoichiometry of the hetero-compound once isolated may notreflect the composition ratios in the mixture from which it wasprepared. On the other hand, most metal alkoxides can be combined toproduce hetero-metallic species that are often more soluble than thestarting materials.

The solvent(s) used can be selected based on a number of criteriaincluding high solubility for the catalyst precursor compound, chemicalinertness to the catalyst precursor compounds, rheological compatibilitywith the deposition technique being used (e.g., the desired viscosity,wettability, solubility, and/or compatibility with other rheologyadjusters), boiling point, vapor pressure, rate of vaporization andeconomic factors (e.g., cost, recoverability, toxicity, etc.).

Suitable solvents used include pentanes, hexanes, cyclohexanes, xylenes,water (e.g., di-ionized water), ethyl acetates, toluene, benzenes,tetrahydrofuran, acetone, carbon disulfide, dichlorobenzenes,nitrobenzenes, pyridine, methyl alcohol, ethyl alcohol, butyl alcohol,chloroform, mineral spirits and mixtures thereof.

According to a preferred method, the supported catalyst particles, onceformed, are incorporated in at least one of tobacco cut filler,cigarette paper and a cigarette filter that are used to form acigarette. By incorporating the supported catalyst particles into one ormore components of a cigarette, the amount of carbon monoxide inmainstream smoke during smoking can be reduced.

As used herein, a catalyst is capable of affecting the rate of achemical reaction, e.g., a catalyst can increase the rate of oxidationof carbon monoxide to carbon dioxide without participating as a reactantor product of the reaction. An oxidant is capable of oxidizing areactant, e.g., by donating oxygen to the reactant, such that theoxidant itself is reduced. A reducing agent is capable of reducing areactant, e.g., by receiving oxygen from the reactant, such that thereducing agent itself is oxidized.

While not wishing to be bound by any particular theory, it is believedthat during smoking of a cigarette having incorporated therein supportedcatalyst particles, CO and/or NO can be catalyzed in the presence ofoxygen to reduce the level of CO and/or NO in mainstream and/orsidestream smoke. It is also believed that subsequent to the catalyticreaction, the supported catalyst particles may oxidize CO in the absenceof oxygen and/or reduce NO to decrease the level of CO and/or NO in themainstream and/or sidestream smoke.

A preferred embodiment of a method of making a cigarette comprisesincorporating supported catalyst particles in and/or on at least one oftobacco cut filler, a cigarette wrapper optionally comprising web-fillermaterial and a cigarette filter comprising filter material; forming atobacco column from the tobacco cut filler in a cigarette makingmachine; placing the cigarette wrapper around the tobacco column to forma tobacco rod of a cigarette; and optionally attaching the cigarettefilter to the tobacco column using tipping paper.

The amount of the supported catalyst incorporated in a cigarette can beselected such that the amount of carbon monoxide and/or nitric oxide inmainstream smoke is reduced during smoking of a cigarette. A totalpreferred amount of catalyst per cigarette is an amount effective toconvert at least some CO to CO₂ and/or convert at least some NO to N₂. Apreferred amount of the catalyst per cigarette is from about 1 to 200mg, from about 1 to 50 mg, or from about 50 to 100 mg.

Preferably, the supported catalyst particles are incorporated in tobaccocut filler, cigarette wrapper and/or a cigarette filter in an amounteffective to reduce the concentration in mainstream smoke of carbonmonoxide and/or nitric oxide by at least 5% (e.g., by at least 15%, 20%,25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or95%). In a most preferred embodiment, the catalysts particles areincorporated in one or more components of a cigarette in an amounteffective to reduce the concentration of carbon monoxide and/or nitricoxide during smoking of the cigarette by at least 10% (e.g., at least20, 30, 40 or 50%). Without wishing to be bound by theory, it isbelieved that the synergy between the catalyst particles and the supportparticles can provide an effective (e.g., low temperature) catalyst forcarbon monoxide and nitric oxide.

“Smoking” of a cigarette means the heating or combustion of thecigarette to form smoke, which can be drawn through the cigarette.Generally, smoking of a cigarette involves lighting one end of thecigarette and, while the tobacco contained therein undergoes acombustion reaction, drawing smoke from the combustion through the mouthend of the cigarette. The cigarette may also be smoked by other means.For example, the cigarette may be smoked by heating a tobacco rodportion of a cigarette using electrical heater means as described incommonly-assigned U.S. Pat. Nos. 6,053,176; 5,934,289; 5,591,368 or5,322,075 or by using heat from a combustible heat source such asdescribed in commonly assigned U.S. Pat. No. 4,966,171.

The term “mainstream smoke” refers to the smoke issuing or drawn throughthe mouth end of a cigarette during smoking of a cigarette. The term“sidestream smoke” refers to smoke produced during static burning.

Several factors contribute to the formation of carbon monoxide andnitric oxide in mainstream tobacco smoke. In addition to the combustionof constituents in the tobacco, the temperature and the oxygenconcentration in a cigarette during combustion can affect theirformation. For example, the total amount of carbon monoxide formedduring smoking comes from a combination of three main sources: thermaldecomposition (about 30%), combustion (about 36%) and reduction ofcarbon dioxide with carbonized tobacco (at least 23%). Formation ofcarbon monoxide from thermal decomposition, which is largely controlledby chemical kinetics, starts at a temperature of about 180° C. andfinishes at about 1050° C. Formation of carbon monoxide and carbondioxide during combustion is controlled largely by the diffusion ofoxygen to the surface (k_(a)) and via a surface reaction (k_(b)). At250° C., k_(a) and k_(b), are about the same. At 400° C., the reactionbecomes diffusion controlled. Finally, the reduction of carbon dioxidewith carbonized tobacco or charcoal occurs at temperatures around 390°C. and above.

During combustion, nitric oxide is produced in mainstream smoke at aconcentration of about 0.5 mg/cigarette. However, nitric oxide can bereduced by carbon monoxide according to the following reactions:

2NO+CO→N₂O+CO₂

N₂O+CO→N₂+CO₂

During smoking there are three distinct regions in a cigarette: thecombustion zone, the pyrolysis/distillation zone, and thecondensation/filtration zone. While not wishing to be bound by anyparticular theory, it is believed that the supported catalyst particlescan target the various reactions that occur in different regions of thecigarette during smoking. The supported catalyst particles can convertCO to CO₂ and/or NO to N₂ in the presence or absence of an externalsource of oxygen.

First, the combustion zone is the burning zone of the cigarette producedduring smoking of the cigarette, usually at the lit end of thecigarette. The temperature in the combustion zone ranges from about 700°C. to about 950° C., and the heating rate can be as high as 500°C./second. The concentration of oxygen is low in the combustion zonebecause oxygen is being consumed in the combustion of tobacco to producecarbon monoxide, carbon dioxide, nitric oxide, water vapor and otherorganic compounds. The low oxygen concentration coupled with the hightemperature leads to the reduction of carbon dioxide to carbon monoxideby the carbonized tobacco. In the combustion zone, the supportedcatalyst particles can oxidize carbon monoxide (to form carbon dioxide)and/or reduce nitric oxide (to form nitrogen). The combustion zone ishighly exothermic and the heat generated is carried to thepyrolysis/distillation zone.

The pyrolysis zone is the region behind the combustion zone, where thetemperature ranges from about 200° C. to about 600° C. The pyrolysiszone is where most of the carbon monoxide is produced. The majorreaction is the pyrolysis (i.e., the thermal degradation) of the tobaccothat produces carbon monoxide, carbon dioxide, nitric oxide, charcoaland other smoke components using the heat generated in the combustionzone. There is some oxygen present in this region, and thus thesupported catalyst particles may catalyze the oxidation of carbonmonoxide to carbon dioxide and/or the reduction of nitric oxide tonitrogen. In the pyrolysis zone the supported catalyst particles canalso directly oxidize CO and/or reduce NO.

In the condensation/filtration zone the temperature ranges from ambientto about 150° C. The major process in this zone is thecondensation/filtration of the smoke components. Some amount of carbonmonoxide, carbon dioxide, nitric oxide and nitrogen diffuse out of thecigarette and some oxygen (e.g., air) diffuses into the cigarette. Thepartial pressure of oxygen in the condensation/filtration zone does notgenerally recover to the atmospheric level. In thecondensation/filtration zone, the supported catalyst particles cancatalyze the conversion of carbon monoxide to carbon dioxide and/ornitric oxide to nitrogen.

During the smoking, mainstream smoke is drawn toward the mouth end ofthe cigarette. As carbon monoxide and nitric oxide travel within thecigarette, oxygen diffuses into and carbon monoxide and nitric oxidediffuse out of the cigarette through the wrapper. After a typical2-second puff of a cigarette, CO and NO are concentrated in theperiphery of the cigarette, i.e., near the cigarette wrapper, in frontof the combustion zone. Due to diffusion of O₂ into the cigarette, theoxygen concentration is also high in the peripheral region. Airflow intothe tobacco rod is greatest near the combustion zone at the periphery ofthe smoking article and is approximately commensurate with the gradientof temperature, i.e., higher airflow is associated with largertemperature gradients. In a typical cigarette, the highest temperaturegradient is from the combustion zone (>850-900° C.) axially toward themouth end of the cigarette. Within a few millimeters behind thecombustion zone the temperature drops to near ambient. Furtherinformation on airflow patterns, the formation of constituents incigarettes during smoking and smoke formation and delivery can be foundin Richard R. Baker, “Mechanism of Smoke Formation and Delivery”, RecentAdvances in Tobacco Science, vol. 6, pp. 184-224, (1980) and Richard R.Baker, “Variation of the Gas Formation Regions within a CigaretteCombustion Coal during the Smoking Cycle”, Beiträge zur TabakforschungInternational, vol. 11, no. 1, pp. 1-17, (1981), the entire contents ofboth of which are incorporated herein by reference.

While direct placement of the supported catalyst particles in thetobacco cut filler is preferred, the supported catalyst particles may beplaced in the cigarette filter, or incorporated in cigarette paper(wrapper). The supported catalyst particles can be placed both in thetobacco cut filler and in other locations. The quantity, location anddistribution in a cigarette of the catalyst particles can be selected asa function of the temperature and airflow characteristics exhibitedduring smoking in order to adjust, e.g., increase or maximize theconversion rate of CO to CO₂ and/or NO to N₂. Furthermore, a catalystcomposition can be selected that operates in a given temperature range,and a catalytically effective amount of the supported catalyst particlescan be incorporated into a component of a cigarette (e.g., tobacco cutfiller, wrapper and/or filter) to control the conversion efficiency.

The supported catalyst particles may be incorporated into at least onecomponent in the form of a dry powder, paste or dispersion in a liquid.For example, catalyst particles in the form of a dry powder can bedusted on cut filler, cigarette paper material or filter material. Adispersion of catalyst material can be sprayed on the cut filler,cigarette wrapper or filter material (including filter paper material orcellulose acetate tow, by way of example).

The supported catalyst particles may be incorporated into the tobaccorod of a cigarette. Preferably the supported catalyst particles areprovided continuously along the length of a tobacco rod, though thesupported catalyst particles can be provided at discrete locations alongthe length of a tobacco rod. Furthermore, the supported catalystparticles may be homogeneously or non-homogeneously distributed alongthe length of a tobacco rod. The supported catalyst particles may beadded to cut filler tobacco stock (e.g., loose cut filler) supplied to acigarette-making machine or incorporated directly on a column of tobaccoat the maker prior to the wrapping of a cigarette wrapper about thetobacco column to form a tobacco rod.

One embodiment provides a method for forming the supported catalystparticles and then depositing the supported catalyst particles on and/orincorporating them in tobacco cut filler, which is then used to form acigarette. Any suitable tobacco mixture may be used for the cut filler.Examples of suitable types of tobacco materials include flue-cured,Burley, Bright, Maryland or Oriental tobaccos, the rare or specialtytobaccos, and blends thereof. The tobacco material can be provided inthe form of tobacco lamina, processed tobacco materials such as volumeexpanded or puffed tobacco, processed tobacco stems such as cut-rolledor cut-puffed stems, reconstituted tobacco materials, or blends thereof.The tobacco can also include tobacco substitutes.

In cigarette manufacture, the tobacco is normally employed in the formof cut filler, i.e., in the form of shreds or strands cut into widthsranging from about 1/10 inch to about 1/20 inch or even 1/40 inch. Thelengths of the strands range from between about 0.25 inches to about 3.0inches. The cigarettes may further comprise one or more flavorants orother additives (e.g., burn additives, combustion modifying agents,coloring agents, binders, etc.) known in the art.

In addition to or in lieu of incorporating the supported catalystparticles in the tobacco rod, the supported catalyst particles may beincorporated in cigarette wrapper before or after the cigarette wrapperis incorporated into a cigarette. The supported catalyst particles maybe incorporated into the cellulosic web of the wrapper by depositing thesupported catalyst particles directly on the cellulosic web and/orcombined with web-filler material that is incorporated in the wrappermaterial.

The supported catalyst particles can be incorporated in cigarette paperby spraying or coating the particles onto a wet base (e.g., cellulosic)web, an intermediate web or a finished web. According to one method,supported catalyst particles in the form of a dry powder are physicallyadmixed with the cigarette paper material during the paper manufacturingprocess.

The supported catalyst particles can be coated and/or printed on atleast one surface of a paper wrapper (e.g., an interior and/or exteriorsurface) to form text or images on the cigarette wrapper. The amount ofcoating, printing and/or the amount of supported catalyst can be variedto adjust the amount of CO and/or NO reduction.

The supported catalyst particles can be incorporated into cigarettewrapping paper by incorporating the catalyst particles directly into thepaper web and/or by incorporating the catalyst particles in web-fillermaterial used in the production of the wrapping wrapper. The web-fillermaterial can include an oxide, a carbonate, or a hydroxide of a GroupII, Group III or Group IV metal, or the web-filler material can beselected from the group consisting of CaCO₃; TiO₂, SiO₂, Al₂O₃, MgCO₃,MgO and Mg(OH)₂.

In practice, the web-filler material serves as an agent for controllingthe permeability of the wrapper (measured typically in units of Coresta,which is defined as the volume of air, measured in cubic centimeters,that passes through one square centimeter of material in one minute at apressure drop of 1.0 kilopascals) and also can serve as a support forthe supported catalyst particles.

A catalyst-modified web-filler comprises supported catalyst particlesincorporated in and/or on particles of web-filler. In a preferredexample, the web-filler material is CaCO₃ or other conventional fillermaterial used in cigarette wrapper manufacture such as such as ALBACAR®5970, which is calcium carbonate commercially available from SpecialtyMinerals of Bethlehem, Pa.

Aqueous slurry of the supported catalyst particles and the web-fillermaterial can be incorporated into the head box of a paper-making machineand the mixture of supported catalyst particles and web filler materialcan be incorporated into cigarette paper during the paper-makingprocess.

The supported catalyst particles and filler can be provided in anydesired ratio, e.g., 10 to 90 wt. % supported catalyst and 90 to 10 wt.% web-filler material. In a preferred embodiment, the amount ofweb-filler material in the wrapper (both catalyst-modified web-fillerand/or web-filler material without catalyst) can be from 3 to 50 wt. %.

A supported catalyst-modified web-filler can be used as all or part ofthe filler material in the wrapper-making processes or can bedistributed directly onto the wrapper, such as by spraying or coatingonto wet or dry base web. In production of a cigarette, the wrapper iswrapped around cut filler to form a tobacco rod portion of the smokingarticle by a cigarette-making machine, which has previously beensupplied or is continuously supplied with tobacco cut filler and one ormore ribbons of wrapper.

A cigarette wrapper can be any wrapping suitable for surrounding the cutfiller, including wrappers containing flax, hemp, kenaf, esparto grass,rice straw, cellulose and so forth. Optional filler materials, flavoradditives, and burning additives can be included in the cigarettewrapper. The wrapper can have more than one layer in cross-section, suchas in a bi-layer wrapper as disclosed in commonly-owned U.S. Pat. No.5,143,098, the entire content of which is herein incorporated byreference.

The supported catalyst particles are capable of converting CO to CO₂ andNO to N₂ at near-ambient temperatures, and therefore can be incorporatedin the filter element of a cigarette. The filter may be a mono filter, adual filter, a triple filter, a single- or multiple-cavity filter, arecessed filter or a free-flow filter. The supported catalyst particlescan be incorporated into one or more filter parts selected from thegroup consisting of a shaped wrapper insert, a plug, a space betweenplugs, cigarette filter wrapper, plug wrap, a cellulose acetate sleeve,a polypropylene sleeve, and a free-flow sleeve. Optionally, cigarettefilters can further comprise additives such as flavorants or adsorbents.

Supported catalyst particles can be incorporated in the wrapper of acigarette wherein the wrapper comprises a first wrapper and a secondoutermost wrapper. Preferably, the supported catalyst particles areincorporated in the first inner wrapper. The total amount of supportedcatalyst in the second outer wrapper is preferably less than 50 mg for agiven single cigarette, more preferably the second outer wrapper doesnot include the supported catalyst particles so as to provide acigarette whose appearance is not affected by coloration from thesupported catalyst particles.

In exemplary embodiments, a total amount of supported catalyst particlesin a cigarette wrapper is from about 1 to 200 mg, preferably at least 50mg per cigarette.

Supported catalyst particles will preferably be distributed throughoutthe tobacco rod, cigarette filter material and/or the cigarette wrapperportions of a cigarette. By providing the supported catalyst throughoutone or more components of a cigarette it is possible to reduce theamount of carbon monoxide drawn through the cigarette, particularly atthe combustion, pyrolysis, condensation and/or filter regions.

A further embodiment provides a method of making a cigarette comprisingthe supported catalyst particles. Techniques for cigarette manufactureare known in the art. Any conventional or modified cigarette makingtechnique may be used to incorporate the catalyst particles. Theresulting cigarettes can be manufactured to any known specificationsusing standard or modified cigarette making techniques and equipment.The cut filler composition is optionally combined with other cigaretteadditives, and provided to a cigarette-making machine to produce atobacco column, which is then wrapped in a cigarette wrapper, andoptionally tipped with filters.

Cigarettes may range from about 50 mm to about 120 mm in length. Thecircumference is from about 15 mm to about 30 mm in circumference, andpreferably around 25 mm. The tobacco packing density is typicallybetween the range of about 100 mg/cm³ to about 300 mg/cm³, andpreferably 150 mg/cm³ to about 275 mg/cm³.

The activity of selected supported catalyst particles can be evaluatedusing a continuous flow packed bed reactor. The reactor comprises aquartz tube positioned within a programmable tube furnace. A test samplecomprising supported catalyst particles can be placed inside the quartztube, which is positioned within the furnace. Thermocouples are used tomonitor the temperature of the furnace and of the supported catalystparticles within the reactor. To evaluate the ability of the supportedcatalyst particles to reduce the concentration of carbon monoxide and/ornitric oxide, a known mass of the catalyst particles can be dusted ontoquartz wool and placed in the middle of the reactor. For the reactordata reported herein, the mass of the catalyst particles is about 50 mg.A filter pad can be used to prevent particulate material from entering agas analyzer, which is located at a downstream side of the reactor. Aninput reactant gas mixture is introduced at an upstream side of thereactor and is passed through the quartz tube and over the catalystparticles at approximately atmospheric pressure at a total gas flow rateof about 1000 ml/min.

An input gas mixture is used to measure the oxidation of CO in thepresence of an external source of oxygen. The test input gas mixtureconsists essentially of about 3.5% CO and 21% O₂ (balance He).

After attaining a steady state flow of gas, the temperature of thefurnace is increased at a heating rate of about 15° C./min. and the gasthat passes over the particles and emerges from the downstream side ofthe reactor is analyzed by a quadrupole mass spectrometer coupled to adata acquisition system. The NLT2000 multi-gas analyzer measures theconcentration of CO, CO₂, NO and O₂ in the gas.

Data from the multi-gas analyzer was plotted as a function of furnacetemperature. The data include the temperature at which about 5% of thecarbon monoxide is converted to carbon dioxide (T₅), the temperature atwhich about 50% of the carbon monoxide is converted to carbon dioxide(T₅₀) and the temperature at which full conversion was obtained (T₁₀₀).

The supported catalyst particles comprise metallic cobalt particlesincorporated in commercially available graphite nanotubes. In a firstexperimental run, the supported catalyst particles can convert 5% of theCO in the test gas stream to CO₂ at a temperature of about 195° C. andcan convert 50% of the CO at a temperature of about 210° C. Nearly 100%conversion of CO is obtained at a sample temperature of about 220° C. Ina subsequent experimental run of the same sample, T₅ was found to beabout 140° C., T₅₀ was about 155° C., and T₁₀₀ was about 160° C.Improvement in the catalytic activity of the sample from the first runto the second run can be attributed to removal of residual moisture fromexposed surfaces of the catalyst and/or support particles.

The supported catalyst particles may be used in a variety ofapplications. For example, the catalyst particles may be incorporatedinto one or more components of a cigarette (e.g., tobacco cut filler,cigarette paper and/or cigarette filters) such that during smoking ofthe cigarette the concentration of carbon monoxide and/or nitric oxidein mainstream and/or sidestream smoke is reduced.

Referring to FIG. 1, a preferred embodiment of a cigarette 100 has atobacco rod portion 90 and filtering tip 92. Optionally, embodiments ofthe cigarette 100 can be practiced without a filtering tip 92.Typically, the tobacco rod portion 90 comprises a column of tobacco 102(e.g., tobacco cut filler). According to an embodiment, as shown inexpanded view in FIG. 1, supported catalyst particles 108 can besupported on the tobacco cut filler 102.

Preferably the tobacco rod 90 is enwrapped with a cigarette (tobacco)wrapper 104. As shown in expanded view in FIG. 2, the wrapper 104includes a web of fibrous cellulosic material 106 in which is optionallydispersed particles of web-filler material 110, such as calciumcarbonate (CaCO₃). According to a further embodiment, supported catalystparticles 108 can be supported on the fibrous web 106. In a stillfurther embodiment, the supported catalyst particles can be supported onfilter material (not shown) comprising filtering tip 92.

The catalyst particles may be incorporated into a hydrocarbon conversionreactor in an amount effective to convert hydrocarbons. The catalystparticles may be incorporated into a vehicle exhaust emissions system inan amount effective to oxidize carbon monoxide to carbon dioxide. Thecatalyst particles may also be used for emissions reduction in the coldstarting of an automobile engine in an amount effective to oxidizecarbon monoxide to carbon dioxide. In another embodiment, the catalystparticles may be incorporated into a laser in an amount effective tooxidize carbon monoxide to carbon dioxide. In another embodiment, thecatalyst particles can be incorporated into a fuel cell in an amounteffective to oxidize carbon monoxide to carbon dioxide. In yet anotherembodiment, the catalyst particles can be used in an air filter for theconversion of carbon monoxide and/or indoor volatile organic compounds.

While the invention has been described with reference to preferredembodiments, it is to be understood that variations and modificationsmay be resorted to as will be apparent to those skilled in the art. Suchvariations and modifications are to be considered within the purview andscope of the invention as defined by the claims appended hereto.

All of the above-mentioned references are herein incorporated byreference in their entirety to the same extent as if each individualreference was specifically and individually indicated to be incorporatedherein by reference in its entirety.

1. The method of claim 14, wherein the catalyst particles are supportedin and/or on electrically conductive support particles of graphiticcarbon or a partially reduced oxide.
 2. The method of claim 1, wherein(a) the catalyst particles comprise nanoscale particles and/or thesupport particles comprise nanoscale particles; (b) the catalystparticles comprise a transition metal or an oxide of a transition metal;(c) the catalyst particles comprise a noble metal or an oxide of a noblemetal; (d) the support particles comprise a graphitic nanostructure; (e)the graphitic carbon comprises carbon nanotubes and at least some of thecatalyst particles are enveloped by the carbon nanotubes; or (f) thesupport particles of graphitic carbon are electrospun.
 3. The method ofclaim 1, wherein the partially reduced oxide comprises a transitionmetal selected from the group consisting of titanium, vanadium,zirconium, niobium, molybdenum, and mixtures thereof and/or thepartially reduced oxide further comprises a dopant that is differentthan the transition metal.
 4. The method of claim 3, wherein the dopantis selected from the group consisting of titanium, vanadium, zirconium,niobium, molybdenum, and mixtures thereof.
 5. The method of claim 1,wherein the partially reduced oxide comprises a Magnéli phase.
 6. Themethod of claim 1, wherein the component is selected from the groupconsisting of tobacco cut filler, cigarette paper and cigarette filtermaterial.
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. A method of making acigarette, comprising: incorporating supported catalyst particles inand/or on at least one of tobacco cut filler, a cigarette wrapperoptionally comprising web-filler material and a cigarette filtercomprising filter material wherein the supported catalyst particlescomprise catalyst particles supported in and/or on support particles;forming a tobacco column from the tobacco cut filler in a cigarettemaking machine; placing the cigarette wrapper around the tobacco columnto form a tobacco rod of a cigarette; and optionally attaching thecigarette filter to the tobacco column using tipping paper.
 15. Themethod of claim 14 , wherein the incorporating comprises spraying,dusting or immersing the supported catalyst particles.
 16. The method ofclaim 14 , wherein the supported catalyst particles are incorporated inthe cigarette wrapper by spraying or coating the catalyst particles ontoa wet base web, intermediate web or finished web.
 17. The method ofclaim 14, wherein the catalyst particles are incorporated in an amounteffective to convert at least 10% of carbon monoxide in mainstreamtobacco smoke to carbon dioxide and/or convert at least 10% of nitricoxide in mainstream tobacco smoke to nitrogen, the incorporatingoptionally comprising combining the catalyst particles and at least oneof the tobacco cut filler, cigarette wrapper and cigarette filtermaterial in the absence of a liquid.
 18. The method of claim 14, whereinthe support particles comprise a graphitic nanostructure.
 19. The methodof claim 14, wherein the support particles comprise carbon nanotubes andat least some of the catalyst particles are enveloped by the carbonnanotubes.
 20. The method of claim 14, wherein the support particlescomprise electrospun graphitic carbon.
 21. A method of oxidizing carbonmonoxide to carbon dioxide comprising contacting catalyst particlessupported in and/or on electrically conductive support particles ofgraphitic carbon or a partially reduced oxide with a gas containingcarbon monoxide, the gas being selected from the group consisting ofmainstream and/or sidestream cigarette smoke, vehicle exhaust emission,a gas used in a laser, a gas used in a fuel cell, and ambient airundergoing air filtration.